Make the memory object simply manage the data pointer and the maxsize and move
the offset and size handling to common functionality.
Use the READONLY flag to set a readonly lock.
Remove the data and size fields from the unmap method. We need an explicit
resize operation instead of using the unmap function.
Make internal helper lock and unlock functions.
Update unit test and users of the old API.
Count how many mappings are currently active and also with what access pattern.
Update the design doc with restrictions on the access patterns for nested
mappings.
Check if nested mappings obey the access mode restrictions of the design doc.
Add various unit tests to check the desired behaviour.
Make an unmap call with a different data pointer than the map call update the
offset field. This allows for both offset and size adjustements in the unmap
call.
